Oil pump system of an engine for a vehicle

ABSTRACT

Reduction of engine power loss and enhancement of fuel consumption may be achieved by an oil pump system of an engine for a vehicle including an oil sump reserving engine oil used for lubrication of the engine, a hydraulic pump pumping the engine oil, a main relief valve that is disposed on an output line of the hydraulic pump and controls an output pressure of the output line depending on the output pressure and a control pressure, and an auxiliary relief valve that redirects the output pressure to the main relief valve as a control pressure depending on operating condition of the engine.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2010-0114507 filed Nov. 17, 2010, the entire contents of which application is incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to oil pump system of an engine for a vehicle engine.

2. Description of Related Art

While various types of hydraulic pumps are used in an engine lubrication system in order to pump incompressible fluid such as engine oil, output pressure and volume of such hydraulic pumps varies depending on the operating speed of an engine since the engine speed varies in a wide speed range.

Output hydraulic pressure of the hydraulic pump of an engine should be controlled to remain in a range of minimum required level to maximum required level, and the maximum required level is achieved at an engine speed much lower than the engine speed limit.

This means that the output hydraulic pressure of the hydraulic pump may become excessive above an intermediate engine speed at which the maximum required pressure level is achieved. The excessive output pressure and volume may negatively affect an engine operation and may damage engine components. In this background, a constant displacement pump such as a gear pump has been proposed to be provided with a pressure relief valve so that excessive oil may be returned to an oil reservoir in order to maintain the output pressure below the maximum required level.

In this background, it would be beneficial if output pressure of a constant displacement pump is precisely controlled within the maximum pressure level.

The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF INVENTION

Various aspects of the present invention provide for an oil pump system of an engine for a vehicle having advantages of active controlling of output oil pressure so as to reduce engine power loss and enhance fuel consumption.

One aspect of the present invention provides an oil pump system of an engine for a vehicle comprising an oil sump reserving engine oil used for lubrication of the engine, a hydraulic pump pumping the engine oil, a main relief valve that is disposed on an output line of the hydraulic pump and controls an output pressure of the output line depending on the output pressure and a control pressure, and an auxiliary relief valve that redirects the output pressure to the main relief valve as a control pressure depending on operating condition of the engine.

The hydraulic pump may be a constant displacement pump. The main relief valve may include an elastic member exerting an elastic force in an opposite direction to which the output pressure and the control pressure is applied.

The main relief valve may further include a valve body and a valve spool. The valve body includes a first port receiving a pressurized oil from the output line, a second port exhausting the oil received through the first port, and a third port receiving a control oil from the auxiliary relief valve. The valve spool includes a first land receiving the oil pressure of the pressurized oil received through the first port and a second land receiving the control oil received through the third port. The elastic member elastic member is arranged between the second land and the valve body so as to exert an elastic force to push the valve spool toward the first port.

The auxiliary relief valve may be controlled by a solenoid valve controlled by an engine control unit. The solenoid valve may be a proportional control solenoid valve and may be duty controlled depending on driving condition of the engine.

The engine control unit duty controls the solenoid valve based on signals from a sensor unit including an engine RPM sensor, an oil temperature sensor, and a coolant temperature sensor.

The auxiliary relief valve may include a valve body and a valve spool installed therein. The valve body of the auxiliary relief valve includes a first port receiving the pressurized oil of the output line, a second port supplying the oil received through the first port to the third port of the main relief valve, and a third port selectively exhausting the oil received through the first port. The valve spool of the auxiliary relief valve includes a first land selectively communicating the first port and the second port and a second land selectively communicating the third port to the first and second ports and in cooperation with the first land.

By such an arrangement of an oil pump system, precise hydraulic pressure is supplied for engine lubrication and damage of engine components due to an unstable lubricant pressure is reduced. In addition, power loss may be reduced and accordingly an enhancement of fuel consumption may be achieved.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a low speed and high temperature state of an exemplary oil pump system of an engine for a vehicle according to the present invention.

FIG. 2 is a schematic diagram illustrating an intermediate speed and intermediate temperature state of an oil pump system of an engine for a vehicle according to the present invention.

FIG. 3 is a schematic diagram illustrating a high speed and low temperature state of an oil pump system of an engine for a vehicle according to the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

FIG. 1 is a schematic diagram illustrating a low speed and high temperature state of an oil pump system of an engine for a vehicle according to various embodiments of the present invention. As shown in FIG. 1, the oil pump system of an engine for a vehicle according to various embodiments of the present invention includes moil sump 2, a hydraulic pump 4, a main relief valve 6, and an auxiliary relief valve 8.

The oil sump 2 is a reservoir of an engine lubricant and may be also called an oil pan.

The hydraulic pump 4 pumps a lubricant such as engine oil from the oil sump 2 in order to supply it to engine components requiring lubrication. The hydraulic pump 4 may be a constant displacement pump such as a gear pump.

When an engine (not shown) starts, the hydraulic pump 4 starts pumping the lubricant in the oil sump 2, and the pumping pressure and volume proportionally depends on a rotation speed of the engine.

The main relief valve 6 and the auxiliary relief valve 8 are disposed in parallel on an output line 10 of the hydraulic pump 4 so as to control an output pressure of the hydraulic pump 4. The output line 10 is connected with a main gallery (not shown) so as to deliver the engine oil to engine components requiring lubrication.

The main relief valve 6 includes a valve body and a valve spool 64 installed therein. The valve body includes a first port 61 receiving a pressurized oil from the output line 10, a second port 62 exhausting the oil received through the first port 61, and a third port 63 receiving a control oil from the auxiliary relief valve 6.

The valve spool 64 includes a first land 65 receiving the oil pressure of the pressurized oil received through the first port 61 and a second land 66 receiving the control oil received through the third port 63. In addition, an elastic member 67 is arranged between the second land 66 and the valve body so as to exert an elastic force to push the valve spool 64 toward the first port 61. By such an arrangement, the first and second ports 61 and 62 selectively communicate depending on movement of the valve spool 64 that is controlled by the oil pressure of the pressurized oil acting the first land 65, the oil pressure of the control oil acting on the third second land 66, and the elastic force of the elastic member 67.

When the pressurized oil of the output line 10 at a pressure higher than the elastic force of the elastic member 67 inflows into the main relief valve 6 through the first port 61, the valve spool 64 starts moving downward in the drawing and thus the first and second ports 61 and 62 communicates so that the pressurized oil of the output line 10 is exhausted through the second port 62.

The exhausted oil from the main relief valve 6 may be returned to the oil sump 2 or to an inlet of the hydraulic pump 4.

When the control oil also inflows into the main relief valve 6 through the third port 63 while the pressurized oil inflows into the main relief valve 6, the control oil pressure is added to the pressurized oil pressure so as to further move the valve spool 64 downward in the drawing. In this case, a communicating passage between the first and second ports 61 and 62 may be enlarged and more amount of oil may be exhausted.

The auxiliary relief valve 8 includes a valve body and a valve spool 84 installed therein. The valve body 84 of the auxiliary relief valve 8 includes a first port 81 receiving the pressurized oil of the output line 10, a second port 82 supplying the oil received through the first port 81 to the third port 63 of the main relief valve 6, and a third port 83 selectively exhausting the oil received through the first port 81.

The valve spool 84 includes a first land 85 selectively communicating the first port 81 and the second port 82 and a second land 86 selectively communicating the third port to the first and second ports 81 and 82 in cooperation with the first land 85. The second land 86 may be connected with a solenoid valve 87 so that the valve spool 84 may be electrically operated.

The solenoid valve 87 may be a proportional control solenoid valve controlled by an engine control unit (ECU) 11, and the ECU 11 duty-controls the solenoid valve 87 based on signals from an engine RPM sensor 12 measuring an engine speed, a fuel amount sensor 14 measuring an amount of fuel injected into the engine, an oil temperature sensor 16 measuring a temperature of the engine oil, and a coolant temperature sensor 18 measuring a coolant of the engine.

The valve spool 84 moves under the control of the solenoid valve 87 controlled by the ECU 11. Depending on the position of the valve spool 84, the oil received through the first port 81 may be either fully supplied to the third port 63 of the main relieve valve 6 through the second port 82 (refer to FIG. 2), or partially supplied to the third port 63 of the main relieve valve 6 while being partially exhausted through the third port 83 (refer to FIG. 3).

According to the oil pump system arranged as above, the output pressure of the hydraulic pump 4 is low at a low speed and high temperature of the engine, and in this case, the solenoid valve 87 may be controlled off, i.e., at a zero (0) duty.

Criteria for the low speed and the high temperature may be set by a person of an ordinary skill in the art considering characteristics of a lubrication system of an engine. The temperature used in these criteria may be an oil temperature directly measured by the oil temperature sensor 16, or an equivalent temperature calculated based on values obtained by the sensors 12, 14, 16, and 18.

In this case, as shown in FIG. 1, the output pressure of hydraulic pump 4 is only controlled by the main relief valve 61, and the output pressure is not sufficient to overcome the elastic force of the elastic member 67. Accordingly, the first and second ports 61 and 62 do not communicate with each other such that the out pressure of the hydraulic pump 4 is fully supplied to engine components.

In an intermediate speed and intermediate temperature range at which the output pressure of the hydraulic pump 4 becomes larger than a predetermined threshold pressure value, the output pressure of the hydraulic pump 4 is controlled to be reduced.

In this case, as shown in FIG. 2, the output pressure of the hydraulic pump 4 acting on the first land 65 of the main relief valve 6 overcomes the elastic force of the elastic member 67 and thus the valve spool 64 moves downward such that the pressurized oil in the output line 10 starts inflowing into the first port 61 and being exhausted through the second port 62.

In addition, ECU 11 starts duty controlling of the solenoid valve 87 based on the signals from the engine RPM sensor 12, the fuel amount sensor 14, the oil temperature sensor 16, and the coolant temperature sensor 18. Depending on the duty applied to the solenoid valve 87, the pressurized oil pressure supplied through the first port 81 is partially redirected to the second port 82 and partially exhausted through the third port 83.

When the duty ratio of the solenoid valve 87 is increased, the oil supplied through the first port 81 is more supplied to the second port 82 than to the third port 83. When a lager ratio of oil is supplied to the second port 82, more control oil is supplied to the third port 63 of the main relief valve 6. In this case, since the valve spool 64 moves further downward, more volume of oil is exhausted through the second port 62 of the main relieve valve 6 causing greater reduction of output pressure of the output line 10.

When the duty ratio of the solenoid valve 87 is decreased, less oil is redirected to the second port 82, and relatively more oil is exhausted through the third port 83. Therefore, pressure reduction of the output pressure of the output line 10 is decreased since less control oil is redirected to the third port 63 of the main relief valve 6.

It is notable that the amount of oil flowing in and out the auxiliary relief valve 8 is relatively small in comparison to the amount of oil flowing in and out the main relief valve 8 since the oil supplied from the auxiliary relief valve 8 to the main relief valve 6 is a control oil. Therefore, the amount of oil exhausted through the auxiliary relief valve 8 does not substantially affect the total amount of oil exhausted in the oil pump system of various embodiments. To the contrary, it should be understood that the amount of oil exhausted by the auxiliary relief valve 8 may be used for more precise tuning of the oil pressure control.

In a high speed and low temperature range low, the output pressure of the hydraulic pump 4 becomes very large and is required to be reduced by a large level.

In this case, as shown in FIG. 3, the ECU 11 controls the solenoid valve 87 at a full duty, i.e., 100% duty ratio. Then, the third port 83 of the auxiliary relief valve 8 is closed and the oil received through the first port 81 is fully supplied to the third port 63 of the main relief valve 6 as a control pressure.

Therefore, in the main relief valve 6, a maximum control pressure is applied to the third port 63 as well as the high output pressure of the output line 10 acts on the first land 65. Accordingly, the valve spool 64 is maximally moved downward so that a maximum amount of oil is exhausted through the second port 62.

According to various embodiments, the ECU 11 varies controlling of the solenoid valve 87 based on signals from the engine RPM sensor 12, the fuel amount sensor 14, the oil temperature sensor 16, and the coolant temperature sensor 18 because they are related to oil viscosity that is closely related to oil pressure.

In more detail, at a same operating speed of a same hydraulic pump, higher output pressure is formed at lower oil temperature since the oil viscosity is higher, and lower output pressure is formed at higher oil temperature since the oil viscosity is lower.

When an engine temperature (i.e., a coolant temperature) is higher, clearance of engine components becomes larger and hydraulic pressure applied to the engine components becomes effectively lower.

That is, the output pressure of the hydraulic pump 4 is proportional to the engine speed measured by the engine RPM sensor 12, and inversely proportional to the oil temperature measured by the oil temperature sensor 14, engine load measured by the coolant temperature sensor 16. An excessive output pressure is formed at high speed, low load, and cold temperature.

In this background, the ECU 11 varies the duty control of the solenoid valve 87, and accordingly actively controls the output pressure of the hydraulic pump 4.

By such an active control of the output pressure for lubrication, engine components may be secured in operating at their optimum condition and damage due to unstable lubricant pressure may be reduced.

Furthermore, power loss caused for stably control the output pressure of the hydraulic pump may be minimized and accordingly fuel consumption of an engine may be enhanced.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

1. An oil pump system of an engine for a vehicle comprising: an oil sump reserving engine oil used for lubrication of the engine; a hydraulic pump pumping the engine oil; a main relief valve disposed in an output line of the hydraulic pump and controls an output pressure of the output line depending on the output pressure and a control pressure; and an auxiliary relief valve that redirects the output pressure to the main relief valve as a control pressure depending on operating condition of the engine.
 2. The oil pump system of claim 1, wherein the hydraulic pump is a constant displacement pump.
 3. The oil pump system of claim 1, wherein the main relief valve comprises an elastic member exerting an elastic force in an opposite direction to which the output pressure and the control pressure is applied.
 4. The oil pump system of claim 3, wherein the main relief valve further comprises: a valve body comprising a first port receiving a pressurized oil from the output line, a second port exhausting the oil received through the first port, and a third port receiving a control oil from the auxiliary relief valve; and a valve spool comprising a first land receiving the oil pressure of the pressurized oil received through the first port and a second land receiving the control oil received through the third port, wherein the elastic member elastic member is arranged between the second land and the valve body so as to exert an elastic force to push the valve spool toward the first port.
 5. The oil pump system of claim 1, wherein the auxiliary relief valve is controlled by a solenoid valve controlled by an engine control unit.
 6. The oil pump system of claim 5, wherein the solenoid valve is a proportional control solenoid valve and is duty controlled depending on driving condition of the engine.
 7. The oil pump system of claim 5, wherein the engine control unit duty controls the solenoid valve based on signals from a sensor unit including an engine RPM sensor, an oil temperature sensor, and a coolant temperature sensor.
 8. The oil pump system of claim 5, wherein the auxiliary relief valve comprises: a valve body comprising a first port receiving the pressurized oil of the output line, a second port supplying the oil received through the first port to the third port of the main relief valve, and a third port selectively exhausting the oil received through the first port. a valve spool comprising a first land selectively communicating the first port and the second port and a second land selectively communicating the third port to the first and second ports and in cooperation with the first land. 